Browsing by Issue Date, starting with "2014-02-01"
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- Molecular mobility, composition and structure analysis in glycerol plasticised chitosan filmsPublication . Fundo, Joana F.; Fernandes, Rui; Almeida, Pedro L.; Carvalho, Alexandra; Feio, Gabriel; Silva, Cristina L. M.; Quintas, Mafalda A. C.This study was developed with the purpose to investigate the effect of polysaccharide/plasticiser concentration on the microstructure and molecular dynamics of polymeric film systems, using transmission electron microscope imaging (TEM) and nuclear magnetic resonance (NMR) techniques. Experiments were carried out in chitosan/glycerol films prepared with solutions of different composition. The films obtained after drying and equilibration were characterised in terms of composition, thickness and water activity. Results show that glycerol quantities used in film forming solutions were responsible for films composition; while polymer/total plasticiser ratio in the solution determined the thickness (and thus structure) of the films. These results were confirmed by TEM. NMR allowed understanding the films molecular rearrangement. Two different behaviours for the two components analysed, water and glycerol were observed: the first is predominantly moving free in the matrix, while glycerol is mainly bounded to the chitosan chain. (C) 2013 Elsevier Ltd. All rights reserved.
- On the ranks of certain monoids of transformations that preserve a uniform partitionPublication . Fernandes, Vítor H.; Quinteiro, TeresaThe rank of a semigroup, an important and relevant concept in Semigroup Theory, is the cardinality of a least-size generating set. Semigroups of transformations that preserve or reverse the order or the orientation as well as semigroups of transformations preserving an equivalence relation have been widely studied over the past decades by many authors. The purpose of this article is to compute the ranks of the monoid OR mxn of all orientation-preserving or orientation-reversing full transformations on a chain with mn elements that preserve a uniform m-partition and of its submonoids OP mxn of all orientation-preserving transformations and OD mxn of all order-preserving or order-reversing full transformations. These three monoids are natural extensions of O mxn, the monoid of all order-preserving full transformations on a chain with mnelements that preserve a uniform m-partition.